Metals and metal alloys that are capable of reacting with hydrogen to form a hydride are known as metal hydrides. Most elemental metals and their associated alloys are capable of reacting with hydrogen to form a hydride. Many of these materials have found application in hydrogen storage, hydrogen recovery from gas mixtures, and energy conversion system. Unfortunately, many of the metal hydrides which exhibit the greatest capacity for storing and releasing hydrogen suffer from disadvantages that have heretofore limited their utility for wide scale use.
One property of metal hydrides is that as the metals and alloys react with hydrogen during repeated cycles of hydrogen absorption and release, the metals and alloys break (decrepitate) into small pieces and particulates on the micron and submicron scale known as “fines.” Where such materials are used as membranes or filters for separating hydrogen from other gases, the generation of fines will decrease the efficiency of the filter and/or result in filter failure. Where hydrogen storage materials are used in packed columns or beds, the production of fines causes excessive resistance to gas flow and to blockages.
A further disadvantage to metal hydride materials is a sensitivity to gaseous poisons such as carbon monoxide, various sulfur compounds, and reactive gases including oxygen. Since commercial hydrogen streams often contain small amounts of these impurities, the use of metal hydrides in such applications has been limited.
In Assignee's commonly owned U.S. Pat. No. 5,958,098 which is incorporated herein by reference, a process is provided in which a metal hydride composition is embedded within a silicon oxide which, via a polymerization process, provides a silica matrix having a series of fine pores which contain therein a metal hydride. The silica pores may be of sufficient pore size to exclude common gaseous poisons while retaining fines may be generated within the silica matrix. While the resulting material has tremendously useful properties, the process of generating the sol-gel metal hydride composite does not lend itself to large-scale commercial production.
Accordingly, there remains room for improvements directed more efficient manufacturing techniques for metal hydride composites as well as compositions of metal hydrides having improved dimensional stability.